Firearms-related injury and sex: a comparative National Trauma Database (NTDB) Study

Background Existing study findings on firearms-related injury patterns are largely skewed towards males, who comprise the majority of this injury population. Given the paucity of existing data for females with these injuries, we aimed to elucidate the demographics, injury patterns, and outcomes of firearms-related injury in females compared with males in the USA. Materials and methods A 7-year (2013–2019) retrospective review of the National Trauma Database was conducted to identify all adult patients who suffered firearms-related injuries. Patients who were males were matched (1:1, caliper 0.2) to patients who were females by demographics, comorbidities, injury patterns and severity, and payment method, to compare differences in mortality and several other post-injury outcomes. Results There were 196 696 patients admitted after firearms-related injury during the study period. Of these patients, 23 379 (11.9%) were females, 23 378 of whom were successfully matched to a male counterpart. After matching, females had a lower rate of in-hospital mortality (18.6% vs. 20.0%, p<0.001), deep vein thrombosis (1.2% vs. 1.5%, p=0.014), and had a lower incidence of drug or alcohol withdrawal syndrome (0.2% vs. 0.5%, p<0.001) compared with males. Conclusion Female victims of firearms-related injuries experience lower rates of mortality and complications compared with males. Further studies are needed to elucidate the cause of these differences. Level of evidence Level III.


INTRODUCTION
2][3] The USA has the highest incidence of firearm fatalities of all developed countries, and firearms-related injuries and mortalities have been rising annually. 2 4 5n the USA, females are 21 times more likely to die from firearm injuries than females in any other developed nations, 6 with previous studies indicating worse outcomes in female patients compared with men. 7 8][11] Studies conducted using national databases have not compared the outcomes for firearm injuries among females to males.As the incidence of firearm violence rises, providers should understand the trauma care needed in female versus male victims of firearms-related injuries. 2 4 5he objectives of this study were to describe the injury characteristics between the two sexes and determine the differences in outcomes in female victims of firearms-related injuries compared with males.

MATERIALS AND METHODS
The National Trauma Database (NTDB) was used to identify all adult patients (18 years or older) who suffered a firearms-related injury between 2013 and 2019.Patients were excluded if they had an Abbreviated Injury Scale (AIS) of 6 in any body region, since these injuries are generally not considered survivable, if they were discharged alive in less than 1 day from admission, or if sex was not registered in NTDB.The retrieved data included patient demographics, clinical characteristics, injury severity, comorbidity, and clinical outcomes.This investigation complies with both the Strengthening the Reporting of Observational Studies in Epidemiology guidelines and the Declaration of Helsinki. 12 13

Statistical analysis
Patients were divided into two groups based on their sex: female or male.All variables were presented before and after propensity score matching.In the unmatched data, continuous, normally distributed variables were summarized using a mean and SD, with the statistical significance of differences being determined using the Student's t-test.Contin

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summarized using a median and IQR, with the statistical significance of differences being calculated using the Mann-Whitney U test.Categorical variables were presented as counts and percentages with differences in the distributions being determined using the Χ 2 test.The primary outcome of interest was in-hospital mortality.Secondary outcomes consisted of hospital length of stay and in-hospital complications.Confounding was managed using propensity score matching.Male patients were matched to female patients at a 1:1 ratio with a caliper of 0.2.Matching was based on age, race, AIS in each body region, comorbidities (history of myocardial infarction, history of angina, congestive heart failure, hypertension, peripheral vascular disease, cerebrovascular disease, diabetes mellitus, chronic renal failure, dementia, chronic obstructive pulmonary disease, smoking status, liver cirrhosis, coagulopathy, receiving chemotherapy for cancer, metastatic cancer, drug use disorder, alcohol use disorder, and major psychiatric illness), and payment method.After matching, the statistical significance of differences between the cohorts was determined using the paired Student's t-test (for normally distributed continuous variables), Wilcoxon signed-rank test (for non-normally distributed continuous variables), or McNemar's test with Bonferroni correction (for categorical variables).Two additional subgroup analyses were also performed.The first analysis only included patients with an Injury Severity Score (ISS) ≥15 to assess differences in the most severely injured patients.The second analysis only included patients who were ≥50 years old to reduce the effect of differing levels of estrogen.
A two-tailed p value of less than 0.05 was considered statistically significant in all analyses.The statistical programming language R (R Foundation for Statistical Computing, Vienna, Austria) was used to perform all calculations and tabulations, using the tidyverse, readxl, writexl, and MatchIt packages. 14

DISCUSSION
In this analysis, we aimed to identify the differences in mortality and outcomes after firearms-related injury in the USA between female and male patients admitted to hospitals.We found that females have a statistically significant survival advantage after firearms-related injury compared with males, despite exhibiting a similar overall injury burden after matching.In addition, a lower need for mechanical ventilation and complication rate were detected in the female cohort of patients who had suffered a firearms-related injury.
Although it was not feasible to explain the mechanism for the positive findings associated with the female sex in this retrospective register study, there are several plausible explanations to these findings.The difference in mortality rate between female and male victims of firearms-related injuries may be due to the survival advantage that females have based on their relative hypercoagulable profile compared with males. 15Additionally, there may be some advantages in hormonal differences between the two sexes.0][21] Although previous studies have also detected an association between female sex and survival after traumatic insults compared with male sex, this association has been proven to be stronger in premenopausal women regardless of injury mechanism. 9 16 22-25emales with firearms-related injuries have also shown to have a lower complication rate compared with males, which could

WHAT IS ALREADY KNOWN ON THIS TOPIC
uous, non-normally distributed variables were

Table 1
Patient demographics and clinical features among men and women with firearms-related wounds Age is measured in years.A patient may have had more than one race.ISS, Injury Severity Score.

Table 2
Comorbidities among males and females with firearms-related wounds

Table 3
Patient outcomes among men and women with firearms-related wounds Length of stay is measured in days.DVT, deep vein thrombosis; ICU, intensive care unit.